1. Field of the Invention
The present invention relates to a vehicle window control system (power window) which opens and closes a vehicle windowpane automatically by an electric motor, and has a mechanism for restricting a motion of the vehicle windowpane when an obstacle is pinched between a vehicle window frame and the vehicle windowpane.
2. Related Art
A conventional power window includes a motor driving load detector for detecting a driving load of an electric motor, which drives a vehicle windowpane, or a window frame sensor for detecting an external force exerted on a vehicle window frame, or the like. When a detected driving load or external force exceeds a predetermined value indicative of an obstacle pinched between the window frame and the windowpane, the windowpane is driven in reverse in the window opening direction.
When an obstacle is pinched between the window frame and the windowpane, an external force exerts on both the window frame and the windowpane. Therefore, if the power window has only either the motor driving load detector or the window frame sensor, the power window may operate erroneously when an external force exerts on the window frame or the windowpane by an intentional action such as a mischief. To overcome the erroneous operation, JP-A-7-4137 proposes to use both the motor driving load detector and the window frame sensor so that the windowpane is driven in reverse only when both the detected driving load and the external force exceed the predetermined values.
In the power window according to JP-A-7-4137, the windowpane may not be driven in reverse even when an obstacle is pinched between the window frame and the windowpane depending on a pinching point of the obstacle.
As shown in FIG. 4, a window frame 2 has a slope portion 2a which is inclined to the moving direction of a windowpane 4. When an obstacle 10 is pinched at the slope portion 2a, an external force F0 exerts on the obstacle (window frame). An F0's component force F1 which is perpendicular to the slope portion 2a exerts on the windowpane 4. A driving load of an electric motor is substantially the same as an F1's component force F3(=F0 cos.sup.2 .theta.) which is toward the window closing direction.
Therefore, when the obstacle 10 is pinched at the slope portion 2a exerting an external force F0 on the obstacle 10 (window frame 2), the component force F3 which exerts on the electric motor as the driving load is smaller than the component force F3 which exerts on the electric motor when the same obstacle is pinched at the window frame 2 other than the slope portion 2a. That is, when the obstacle 10 is pinched at the slope portion 2a, the motor load detector can not detect the pinched obstacle 10 unless an external force exerted on the slope portion 2a exceeds F0. As shown in FIGS. 5A and 5B, the external force F0 required for reversing rotation of the electric motor is larger at points (b) and (c) of the slope portion 2a than other points (a) and P.
Further, because the component force F3 exerted on the electric motor as the driving load is small at the slope portion 2a, it is difficult for the motor driving load detector to distinguish driving load detection errors and changes in driving load, which is caused by the pinched obstacle 10. This results in increase in a ratio of the detection error to the detected driving load. Therefore, when the obstacle 10 is pinched at the slope portion 2a of the window frame 2, the power window operates erroneously due to the increase of the detection error of the detected driving load.